(-1乘2)+(-1/2乘3)+·······+(-1/2010乘1/2011)等于
问题描述：
(-1乘2)+(-1/2乘3)+·······+(-1/2010乘1/2011)等于
答
知识点：1/n(n+1)=1/n-1/(n+1)
原式=-(1-1/2+1/2-1/3+1/3-1/4+……+1/2010-1/2011)
=-(1-1/2011)
=-2010/2011